Oi. The base timing on Ford fuel injected motors is not something you should mess with. The timing is controlled by the computer. You need to disconnect the SPOUT connector and set your base timing to 10 BTDC, lock down the distributor AND DON'T TOUCH IT.
It isn't like the old carbed engines where the timing control was completely independent of the carb and you could play with base timing, advance curves, and vacuum advance. The computer controls it all and isn't happy when you play with it. Setting the timing anything other than stock specs make the computer try and compensate and it screws everything up.
Time to school you a bit about Ford fuel injection. you can't be working on your fuel injected motor thinking it is like a carbed motor. At best, you will waste time and money, at worst, you will damage something.
First, learn how to run a self-test of your engine systems
HERE. The factory computer does a fair job diagnosing problems it has, and you can get the trouble codes and run the tests very easily without special tools.
Once you have codes, see what they mean
HERE and
HEREHere is how you set your base timing. Your 300 has an EEC-IV ignition system.
There is loads of free info about the Ford EFI systems on
www.fordfuelinjection.com. It is worth your while to spend some time reading some of those articles and learning about your fuel injection and ignition systems.
Good luck, and don't be afraid to ask questions.